Breeding, husbandry, veterinary care, and hematology of marsh rice rats (Oryzomys palustris), a small animal model for periodontitis

Abstract

Rice rats (Oryzomys palustris) are a recognized animal model for studying periodontal disease and the photoperiodic regulation of reproduction. Here we share information regarding the breeding, husbandry, veterinary care, and hematologic findings about this animal species to facilitate its use in studies at other research institutions. Rice rats initially were quarantined and monitored for excluded pathogens by using microbiologic, parasitologic, and serologic methods with adult female Mus musculus and Rattus norvegicus sentinel animals. Breeders were paired in a monogamous, continuous-breeding system. Rats were housed in static filter-top cages, maintained on commercial chow under 14:10-h light:dark cycles at 68 to 79 °F (20.0 to 26.1 °C) and 30% to 70% humidity. Rice rats apparently adapt relatively well to standard laboratory conditions, despite their aggressive behavior toward conspecifics and humans. Our analysis of 97 litters revealed that dams gave birth to an average of 5.2 pups per dam and weaned 4.2 pups per dam. Several procedures and biologic reagents normally used in standard laboratory rodents (mice and rats) can be used with rice rats. In addition, we present hematologic and serum chemistry values that can be used as preliminary reference values for future studies involving rice rats.

Figure 1.

Daily aspects of the housing and husbandry of rice rats. (A) Animal rack containing pair of breeders in static filter-top cages. (B) Male rice rat approaching a female rat minutes after they were paired. (C) A breeder cage containing a male rat in the entrance of a “to-go cup,” which is used as a rearing shelter; the female rat and pups are hidden inside the shelter. (D) The scruff method is used to restrain a rice rat when it needs to be checked or injected.

Figure 2.

Oxyurid nematodes of the genus Syphacia were identified in rice rats during the quarantine period. Adult parasites were identified on perianal tapes and in cecal contents from sentinels and breeder rice rats. Wet mount sample from cecum; bar, 250 μm.

Figure 3.

Characteristics of the periodontitis model in rice rats. Comparative images stained with methylene blue to delineate the cementoenamel (junction (red arrows) from the maxillary palatal surface of male rice rats fed the standard (standard) or high-sucrose and -casein (H-SC) diet for (A and B) 12 wk or (C and D) 18 wk. The green arrowheads depict the borders of the alveolar bone crest. The blue-stained area corresponds to the area of exposed tooth root which can serve as an index of horizontal alveolar bone height. The H-SC diet increases alveolar bone loss in rice rats. The methylene-blue–stained palatal surfaces of standard or H-SC diet rats for (A and B) 12 wk and (C and D) 18 wk show that rice rats present increased horizontal alveolar bone loss both over time and with H-SC diet feeding. In comparative reconstructed microCT images taken from the mandibles of female rice rats fed the (E) standard or (F) H-SC diets for 12 wk, note the increased vertical alveolar bone loss at the lingual surface in the interproximal spaces of mandibular molars (M) 1 and M2 and M2–M3 in a rat fed the (F) H-SC diet compared with (E) an age-matched control rat. Red arrows indicate the cementoenamel junction, and green arrows point to the alveolar bone crest. (H) Increased mandibular vertical alveolar bone loss (green vertical line) at the interproximal alveolar bone at M1–M2 in a male rat fed the H-SC diet for 18 wk compared with (G) an age-matched control rat fed the standard diet. Methacrylate-embedded section stained en bloc with basic fuchsin. Bar, 200 μm (G and H).

Figure 4.

Histologic features of periodontitis in rice rats. Photographs taken at the interproximal space between the first and second mandibular molars of rice rats fed standard (standard) or high-sucrose and -casein (H-SC) diets for 18 wk. Bacterial plaques (*) were present in both (A) the rats fed the standard diet and (B) those fed the H-SC diet. (B) Periodontal lesions typically were moderate in rice rats fed the H-SC diet for 18 wk; mild migration of the junctional epithelium (black arrow), hyperplasia of the gingival epithelium (EH), and mild inflammatory cell infiltration in the lamina propria (†) also are present in this sample. Hematoxylin and eosin stain; bar, 125 μm.